Advancements in Understanding Airway Diseases

Breathe in, breathe out. One of the main functions that keep us (and the horses we love) alive is also one of the easiest and mindless tasks we carry out on a daily basis. But for horses with airway diseases, breathing is more difficult than it seems. Recently, researchers have made strides in understanding these diseases and what helps (or does not help) control them.

"Inflammatory airway disease (IAD) is the second most common cause of loss of use in young racing Thoroughbreds," noted Laurent Couetil, DVM, PhD, Dipl. ACVIM, professor of large animal medicine and equine sports medicine director at Purdue University, during a presentation at the 2011 American College of Veterinary Internal Medicine Forum, held June 15-18 in Denver, Colo. Inflammatory airway disease affects horses of all breeds and disciplines and is performance limiting due to excess mucus accumulation in the trachea, which reduces the horse's oxygen availability during exercise.

Couetil explained that IAD is caused by exposure to particulates and irritants in the stabling environment, adding that horses housed outside generally don't suffer from airway inflammation. In an indoor environment inhaled irritants, allergens, and ammonia fumes from urine breakdown are known to trigger airway inflammation even in otherwise healthy horses, particularly in combination with endotoxins.

Couetil described a recent study in which researchers evaluated 20 healthy Thoroughbred horses 16-24 months of age with no prior history of racing or IAD. Within three days of arrival at a race training barn, 55% had some degree of IAD, and by Day 28, only two of the 20 remained IAD-free. The researchers determined that both respirable dust in the horses' breathing zones and ammonia accumulation in the stalls led to inflammatory changes in their airways--likely due to a horse's immune responses to the challenge of environmental contaminants. More so, he noted that although the research team placed a HEPA filtration unit over half the horses' stalls, the apparatus was not effective in removing dust or ammonia from the environment.

Couetil discussed a second study that compared the efficacy of two hand-held delivery devices (Aerohippus and Equine Haler) used to administer albuterol (an aerosol bronchodilator designed to relax the muscles around airway, improving lung function) to horses with recurrent airway obstruction (RAO, also known as heaves). Horses with RAO have recurrent episodes of inflammation, cough, mucus, airway constriction, and difficulty breathing. Couetil explained that aerosolized treatment of RAO minimizes side effects (including suppression of the immune system, laminitis, and Cushing's-like signs) seen with systemic administration of bronchodilators.

There was no significant difference between how the two types of bronchodilators administered the albuterol, Couetil explained; however, response to treatment was more consistent when horses were medicated with the Aerohippus product as opposed to the Equine Haler product.

In general, Couetil emphasized that owners and veterinarians can achieve effective results when treating RAO-affected horses using either aerosolized albuterol device. He added that an average dose of 560 micrograms of albuterol was required for maximum effect.

About the Author

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado,
and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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